(a) Technical Field
The present invention relates to an electrode for a fuel cell. More particularly, it relates to an electrode having a pore structure of various sizes and distributions while maintaining an appropriate catalyst layer and pore structure during the operation of a fuel cell.
(b) Background Art
A fuel cell is an electricity-generating device that electrochemically converts chemical energy of fuel into electrical energy in a fuel cell stack instead of converting chemical energy of fuel into heat by combustion. Fuel cells may not only provide power for industries, households, and vehicles, but may also be applied to power supply for small-sized electrical/electronic products, particularly, portable devices.
Currently, Polymer Electrolyte Membrane Fuel Cells (PEMFCs) having a higher power density are being extensively studied as a power supply source for driving vehicles. PEMFCs have a quick startup time and a quick power conversion response time due to a low operating temperature.
Such a polymer electrolyte membrane fuel cell includes a Membrane-Electrode Assembly (MEA) with catalyst electrodes attached to both sides of a polymer electrolyte membrane through which hydrogen ions move, a Gas Diffusion Layer (GDL) for evenly distributing reaction gases and serving to deliver electrical energy that is generated, gaskets and coupling members for maintaining airtightness of reaction gases and cooling water and appropriate coupling pressure, and a bipolar plate that allows the reaction gases and the cooling water to move.
When a fuel cell stack is assembled using such a unit cell, a combination of a membrane-electrode assembly and a gas diffusion layer as a main component is located at the innermost portion thereof. The membrane-electrode assembly includes catalyst electrode layers, i.e., cathode and anode with a catalyst coated on both surfaces of the polymer electrolyte membrane, which allows hydrogen (fuel) and oxygen (oxidant) to react with each other. In addition, gas diffusion layers and gaskets are stacked on the outside of the cathode and the anode.
On the other hand, when a membrane-electrode assembly is fabricated by bonding the catalyst electrodes to the both surfaces of the polymer electrolyte membrane, the catalyst layer structure of the catalyst electrode and the core structure are controlled by membrane-electrode assembly fabrication methods such as decal transfer method, screen print method, brush method, inkjet method, and spray method.
Currently, methods available for mass production of membrane-electrode assemblies are limited to the decal transfer method and the screen print method. The decal transfer method includes coating catalyst slurry on the surface of a release film and then drying the catalyst slurry to form a catalyst electrode layer, stacking a release film with a catalyst layer on both surfaces of an electrolyte membrane, and transferring the catalyst layer to both surfaces of the electrolyte membrane using a hot pressing method.
In a method for fabricating a membrane-electrode assembly suitable for mass production, a pore former is used to control a catalyst layer structure of a catalyst electrode and a pore structure. However, there is a difficulty in removing the pore former.
The use of organic solvents or heat-treatment in a process of removing the pore former affects other components such as the catalyst, and is time-consuming.
In a typical catalyst electrode structure in which catalyst is fixed on a carbon support, since the carbon support corrodes due to the long time operation of a fuel cell, the catalyst layer structure and the pore structure may be deformed, and corrosion and burning damage of the carbon support may cause a loss of active platinum catalyst.
In a method of using a gas diffusion layer formed of carbon fiber as an electrode to support a thin catalyst layer, there is a limitation in mobility of material due to a difference of pore size between the catalyst layer and the electrode (gas diffusion layer).
Also, there is a limitation of excessive interface resistance and interface separation between a catalyst layer and an electrode (gas diffusion layer). Although attempts to improve the mobility of material and minimize the interface resistance with the catalyst layer using a microporous layer are being made, there is still a difficulty in controlling the hydrophilic property and pore structure of the microporous layer.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.